To fabricate and test a non-cytotoxic, chemically inert, hermetically sealed high acuity epi-retinal prosthesis made out of diamond.

Methods

Diamond Microelectrode Array Fabrication: Electrical feedthroughs were made on an electrically insulating polycrystalline diamond (PCD) substrate using pulsed laser milling and electrically conducting nitrogen incorporated ultrananocrystalline diamond (N-UNCD) was grown on top of it using microwave enhance chemical vapour deposition technique. Finally, the N-UNCD electrodes were electrically isolated by pulsed laser milling followed by oxygen plasma cleaning. Metallisation and Integration with electronics: Gold active braze alloy brazing was performed in vacuum to fill the back of the electrical feedthroughs for under bump metallisation and the annulus for laser micro-welding. The back of the electrode feedthroughs were bonded with the microelectronic chip using an indium flipchip bonding technique. Encapsulation: A lid was fabricated from solid polycrystalline diamond and then hermetically micro-welded to the microelectrode array coupled with the chip. The hermeticity of the array and welded capsule were tested using a helium leak tester by attaching the electrode array to a Viton® O-ring.

Results

A rat cortical neuron grown on N-UNCD, PCD and tissue culture plastic (TCP) for 24 h showed that neurons survived in high numbers on both N-UNCD and PCD compared to TCP. This result indicates that neither forms of diamond is cytotoxic. Electrical testing showed that the average isolation over all electrode pairs was about 500 MΩ. The helium leak rate measured through the hermetic arrays and welded capsule is less than the detection limit of the helium leak tester (1x10-11 mbar L s-1 ). Fig1(a) is the SEM image of the electrode and Fig1(b) shows the nanostructrued surface of the electrode.

Conclusions

A high density diamond epi-retinal prosthesis prototype with non cytotoxic diamond material was fabricated and tested successfully. The use of a single material for construction of the array and encapsulation eliminates any potential materials mismatches that could lead to device failure.